1. Field of the Invention
This invention relates to a synchronizer ring in a manual transmission for an automotive vehicle or in a synchronizing device for a synchronous meshing type speed change gear mounted in a machine for construction or agriculture, and a shaping apparatus and a shaping method therefor, and in particular to a synchronizer ring with a frictional material having oil grooves, and a shaping apparatus and a shaping method therefor.
2. Related Background Art
There have heretofore been proposed various synchronizing devices of the inertia lock type having a synchronizer ring with a frictional material such as a porous frictional material provided on the frictional surface thereof.
Where a frictional material is thus used, lubricating oil such as transmission oil is not quickly eliminated from the frictional surface during the shift operation, and this has led to the problem that undersynchro is liable to occur. Therefore, devices have been proposed using a synchronizer ring having a plurality of oil grooves formed on the frictional surface by machining such as cut-machining after the frictional material is bonded to the frictional surface.
For example, FIGS. 1 to 3 of the accompanying drawings show a prior art structure of the type just described, wherein a synchronizer ring 20 has a frictional material 21 bonded thereto and the inner surface thereof forms a frictional surface. On the frictional surface of the frictional material 21, a plurality of longitudinal grooves 22 and two circumferential grooves 23 are formed as oil grooves. In the case of this example, the longitudinal grooves 22 are formed by a hot pressure molding method or the like simultaneously with or after the bonding of the frictional material 1, and the circumferential grooves 23 are thereafter formed by a cutting tool by the use of a lathe.
However, the formation of oil grooves by such a process poses the following problems.
Since the circumferential grooves 23 are formed by cut-machining, the machined shape is not stable due to the irregularity of the then fixed position with respect to the lathe or the like, the irregularity of the machining work, etc., and this has sometimes led to abnormality of the cross-sectional shape such as machining burr or machining crack. Also, in the machined cross-section, as seen in FIG. 3, the fiber layer of the frictional material 21 is exposed and becomes discontinuous.
Accordingly, during use when the frictional material 21 is subject to an input having two components, i.e., a compression force and a shearing force, the frictional material 21 causes concentration of stress in the machined cross-section thereof, and this leads to premature exfoliation of the fiber layer and poor service life.
Also, this machining work is often carried out manually in another step after the pressure molding and therefore, has reduced production efficiency and has complicated quality control, and further has made it difficult to make low cost products.